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 #include &lt;QtGui&gt;

 #include &quot;diagramscene.h&quot;
 #include &quot;arrow.h&quot;

 DiagramScene::DiagramScene(QMenu *itemMenu, QObject *parent)
     : QGraphicsScene(parent)
 {
     myItemMenu = itemMenu;
     myMode = MoveItem;
     myItemType = DiagramItem::Step;
     line = 0;
     textItem = 0;
     myItemColor = Qt::white;
     myTextColor = Qt::black;
     myLineColor = Qt::black;
 }

 void DiagramScene::setLineColor(const QColor &amp;color)
 {
     myLineColor = color;
     if (isItemChange(Arrow::Type)) {
         Arrow *item =
             qgraphicsitem_cast&lt;Arrow *&gt;(selectedItems().first());
         item-&gt;setColor(myLineColor);
         update();
     }
 }

 void DiagramScene::setTextColor(const QColor &amp;color)
 {
     myTextColor = color;
     if (isItemChange(DiagramTextItem::Type)) {
         DiagramTextItem *item =
             qgraphicsitem_cast&lt;DiagramTextItem *&gt;(selectedItems().first());
         item-&gt;setDefaultTextColor(myTextColor);
     }
 }

 void DiagramScene::setItemColor(const QColor &amp;color)
 {
     myItemColor = color;
     if (isItemChange(DiagramItem::Type)) {
         DiagramItem *item =
             qgraphicsitem_cast&lt;DiagramItem *&gt;(selectedItems().first());
         item-&gt;setBrush(myItemColor);
     }
 }

 void DiagramScene::setFont(const QFont &amp;font)
 {
     myFont = font;

     if (isItemChange(DiagramTextItem::Type)) {
         QGraphicsTextItem *item =
             qgraphicsitem_cast&lt;DiagramTextItem *&gt;(selectedItems().first());
         item-&gt;setFont(myFont);
     }
 }

 void DiagramScene::setMode(Mode mode)
 {
     myMode = mode;
 }

 void DiagramScene::setItemType(DiagramItem::DiagramType type)
 {
     myItemType = type;
 }

 void DiagramScene::editorLostFocus(DiagramTextItem *item)
 {
     QTextCursor cursor = item-&gt;textCursor();
     cursor.clearSelection();
     item-&gt;setTextCursor(cursor);

     if (item-&gt;toPlainText().isEmpty()) {
         removeItem(item);
         item-&gt;deleteLater();
     }
 }

 void DiagramScene::mousePressEvent(QGraphicsSceneMouseEvent *mouseEvent)
 {
     if (mouseEvent-&gt;button() != Qt::LeftButton)
         return;

     DiagramItem *item;
     switch (myMode) {
         case InsertItem:
             item = new DiagramItem(myItemType, myItemMenu);
             item-&gt;setBrush(myItemColor);
             addItem(item);
             item-&gt;setPos(mouseEvent-&gt;scenePos());
             emit itemInserted(item);
             break;
         case InsertLine:
             line = new QGraphicsLineItem(QLineF(mouseEvent-&gt;scenePos(),
                                         mouseEvent-&gt;scenePos()));
             line-&gt;setPen(QPen(myLineColor, 2));
             addItem(line);
             break;
         case InsertText:
             textItem = new DiagramTextItem();
             textItem-&gt;setFont(myFont);
             textItem-&gt;setTextInteractionFlags(Qt::TextEditorInteraction);
             textItem-&gt;setZValue(1000.0);
             connect(textItem, SIGNAL(lostFocus(DiagramTextItem *)),
                     this, SLOT(editorLostFocus(DiagramTextItem *)));
             connect(textItem, SIGNAL(selectedChange(QGraphicsItem *)),
                     this, SIGNAL(itemSelected(QGraphicsItem *)));
             addItem(textItem);
             textItem-&gt;setDefaultTextColor(myTextColor);
             textItem-&gt;setPos(mouseEvent-&gt;scenePos());
             emit textInserted(textItem);
     default:
         ;
     }
     QGraphicsScene::mousePressEvent(mouseEvent);
 }

 void DiagramScene::mouseMoveEvent(QGraphicsSceneMouseEvent *mouseEvent)
 {
     if (myMode == InsertLine &amp;&amp; line != 0) {
         QLineF newLine(line-&gt;line().p1(), mouseEvent-&gt;scenePos());
         line-&gt;setLine(newLine);
     } else if (myMode == MoveItem) {
         QGraphicsScene::mouseMoveEvent(mouseEvent);
     }
 }

 void DiagramScene::mouseReleaseEvent(QGraphicsSceneMouseEvent *mouseEvent)
 {
     if (line != 0 &amp;&amp; myMode == InsertLine) {
         QList&lt;QGraphicsItem *&gt; startItems = items(line-&gt;line().p1());
         if (startItems.count() &amp;&amp; startItems.first() == line)
             startItems.removeFirst();
         QList&lt;QGraphicsItem *&gt; endItems = items(line-&gt;line().p2());
         if (endItems.count() &amp;&amp; endItems.first() == line)
             endItems.removeFirst();

         removeItem(line);
         delete line;

         if (startItems.count() &gt; 0 &amp;&amp; endItems.count() &gt; 0 &amp;&amp;
             startItems.first()-&gt;type() == DiagramItem::Type &amp;&amp;
             endItems.first()-&gt;type() == DiagramItem::Type &amp;&amp;
             startItems.first() != endItems.first()) {
             DiagramItem *startItem =
                 qgraphicsitem_cast&lt;DiagramItem *&gt;(startItems.first());
             DiagramItem *endItem =
                 qgraphicsitem_cast&lt;DiagramItem *&gt;(endItems.first());
             Arrow *arrow = new Arrow(startItem, endItem);
             arrow-&gt;setColor(myLineColor);
             startItem-&gt;addArrow(arrow);
             endItem-&gt;addArrow(arrow);
             arrow-&gt;setZValue(-1000.0);
             addItem(arrow);
             arrow-&gt;updatePosition();
         }
     }
     line = 0;
     QGraphicsScene::mouseReleaseEvent(mouseEvent);
 }

 bool DiagramScene::isItemChange(int type)
 {
     foreach (QGraphicsItem *item, selectedItems()) {
         if (item-&gt;type() == type)
             return true;
     }
     return false;
 }</pre>
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